The present invention relates to engines for motorcycles and the like, and in particular to an oil pump assembly and related method therefor.
Twin cam style engines are well known in the motorcycle industry, and employ two separate camshafts to control the valve trains for two cylinder motorcycle engines, such as that disclosed in U.S. Patent Document 2004/0159496. Some twin cam style motorcycle engines, such as those disclosed in U.S. Pat. Nos. 6,047,667 and 6,116,205, drive the two camshafts with a chain drive arrangement. However, for high performance motorcycle engines, a gear drive arrangement for the camshafts is normally preferred, so as to improve valve timing accuracy by eliminating timing chain lash, and variations caused by loose fittings between the drive chain and associated drive chain sprockets. Such gear drive systems result in more horsepower by eliminating chain drag, permit more aggressive cam profiles that result in additional valve lift, and also permit increased valve spring force to be used in the engine heads.
Furthermore, twin cam style motorcycle engines, such as those disclosed in U.S. Pat. Nos. 6,047,667 and 6,116,205, are typically equipped with two or more separate gerotor-type pumps to circulate oil through the engine and to and from a remote oil reservoir. These types of oil pump arrangements add additional complexity and cost to the engine construction, and generally detract from the type of compact engine design usually preferred by motorcycle manufacturers.